Pitch-based carbon foam and composites and uses thereof

ABSTRACT

A thermally conductive carbon foam is provided, normally having a thermal conductivity of at least 40 W/m·K. The carbon foam usually has a specific thermal conductivity, defined as the thermal conductivity divided by the density, of at least about 75 W·cm 3 /m·°K·gm. The foam also has a high specific surface area, typically at least about 6,000 m 2 /m 3 . The foam is characterized by an x-ray diffraction pattern having “doublet” 100 and 101 peaks characterized by a relative peak split factor no greater than about 0.470. The foam is graphitic and exhibits substantially isotropic thermal conductivity. The foam comprises substantially ellipsoidal pores and the mean pore diameter of such pores is preferably no greater than about 340 microns. Other materials, such as phase change materials, can be impregnated in the pores in order to impart beneficial thermal properties to the foam. Heat exchange devices and evaporatively cooled heat sinks utilizing the foams are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is (1) a continuation-in-part of U.S. application Ser.No. 09/136,596 filed Aug. 19, 1998 now U.S. Pat. No. 6,387,343, which isa divisional of U.S. application Ser. No. 08/921,875 filed Sep. 2, 1997,now U.S. Pat. No. 6,033,506; and (2) a continuation-in-part of U.S.application Ser. No. 09/458,640 filed Dec. 9, 1999, which itself is acontinuation-in-part of U.S. application Ser. No. 09/093,406 filed Jun.8, 1998, now U.S. Pat. No. 6,037,032, which itself is acontinuation-in-part of both U.S. application Ser. No. 08/923,877 filedSep. 2, 1997, abandoned, and U.S. application Ser. No. 08/921,875 filedSep. 2, 1997, now U.S. Pat. No. 6,033,506; and (3) acontinuation-in-part of U.S. application Ser. No. 09/093,406 filed Jun.8, 1998, now U.S. Pat. No. 6,037,032, which itself is acontinuation-in-part of both U.S. application Ser. No. 08/923,877 filedSep. 2, 1997, abandoned, and U.S. application Ser. No. 08/921,875 filedSep. 2, 1997, now U.S. Pat. No. 6,033,506; and (4) acontinuation-in-part of U.S. application Ser. No. 08/921,875 filed Sep.2, 1997, now U.S. Pat. No. 6,033,506.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The United States Government has rights in this invention pursuant tocontract No. DE-AC05-96OR22464 between the United States Department ofEnergy and Lockheed Martin Energy Research Corporation.

BACKGROUND OF THE INVENTION

The present invention relates to carbon foam and compposites, and moreparticularly to a process for producing them.

The extraordinary mechanical properties of commercial carbon fibers aredue to the unique graphitic morphology of the extruded filaments. SeeEdie, D. D., “Pitch and Mesophase Fibers,” in Carbon Fibers, Filamentsand Composites, Figueiredo (editor), Kluwer Academic Publishers, Boston,pp. 43-72 (1990). Contemporary advanced structural composites exploitthese properties by creating a disconnected network of graphiticfilaments held together by an appropriate matrix. Carbon foam derivedfrom a pitch precursor can be considered to be an interconnected networkof graphitic ligaments or struts, as shown in FIG. 1. As suchinterconnected networks, they represent a potential alternative as areinforcement in structural composite materials.

Typical processes for producing carbon foams utilize a blowing techniqueto produce a foam of the pitch precursor in which the pitch is meltedand passed from a high pressure region to a low pressure region.Thermodynamically, this produces a “Flash,” thereby causing the lowmolecular weight compounds in the pitch to vaporize (the pitch boils),resulting in a pitch foam. See Hagar, Joseph W. and Max L. Lake, “NovelHybrid Composites Based on Carbon Foams,” Mat. Res. Soc. Symp.,Materials Research Society, 270:29-34 (1992), Hagar, Joseph W. and MaxL. Lake, “Formulation of a Mathematical Process Model Process Model forthe Foaming of a Mesophase Carbon Precursor,” Mat. Res. Soc. Symp.,Materials Research Society, 270:35-40 (1992), Gibson, L. J. and M. F.Ashby, Cellular Solids: Structures & Properties, Pergamon Press, NewYork (1988), Gibson, L. J., Mat. Sci. and Eng A110, 1 (1989),Knippenberg and B. Lersmacher, Phillips Tech. Rev., 36(4), (1976), andBonzom, A., P. Crepaux and E. J. Moutard, U.S. Pat. No. 4,276,246,(1981). Then, the pitch foam must be oxidatively stabilized by heatingin air (or oxygen) for many hours, thereby, cross-linking the structureand “setting” the pitch so it does not melt during carbonization. SeeHagar, Joseph W. and Max L. Lake, “Formulation of a Mathematical ProcessModel Process Model for the Foaming of a Mesophase Carbon Precursor,Mat. Res. Soc. Symp., Materials Research Society, 270:35-40 (1992) andWhite, J. L., and P. M. Shaeffer, Carbon, 27:697 (1989). This is a timeconsuming step and can be an expensive step depending on the part sizeand equipment required. The “set” or oxidized pitch is then carbonizedin an inert atmosphere to temperatures as high as 1100° C., followed bysubjection to temperatures as high as 3000° C. to produce a graphiticcarbon foam.

Other techniques utilize a polymeric precursor, such as phenolic,urethane, or blends of these with pitch. See Hagar, Joseph W. and Max L.Lake, “Idealized Strut Geometries for Open-Celled Foams,” Mat. Res. Soc.Symp., Materials Research Society, 270:41-46 (1992), Aubert, J. W., (MRSSymposium Proceedings, 207:117-127 (1990), Cowlard, F. C. and J. C.Lewis, J. of Mat. Sci., 2:507-512 (1967) and Noda, T., Inagaki and S.Yamada, J. of Non-Crystalline Solids, 1:285-302, (1969). High pressureis applied and the sample is heated. At a specified temperature, thepressure is released, thus causing the liquid to foam as volatilecompounds are released. The polymeric precursors are cured and thencarbonized without a stabilization step. However, these precursorsproduce a “glassy” or vitreous carbon which does not exhibit graphiticstructure and, thus, has low thermal conductivity and low stiffness. SeeHagar, Joseph W. and Max L. Lake, “Idealized Strut Geometries forOpen-Celled Foams,” Mat. Res. Soc. Symp., Materials Research Society,270:41-46 (1992).

In either case, once the foam is formed, it is then bonded in a separatestep to the facesheet used in the composite. This can be an expensivestep in the utilization of the foam.

The process of this invention overcomes these limitations, by notrequiring a “blowing” or “pressure release” technique to produce thefoam. Furthermore, an oxidation stabilization step is not required, asin other methods used to produce pitch-based carbon foams. This processis less time consuming, and therefore, will be lower in cost and easierto fabricate. Moreover, the foam can be produced with an integratedsheet of high thermal conductivity carbon on the surface of the foam,thereby producing a carbon foam with a smooth sheet on the surface toimprove heat transfer.

The present invention further relates to a thermally-conductive foammaterial derived from carbonaceous precursor, and more particularly to athermally conductive, pitch-derived carbon foam having high thermalconductivity and heat exchanging properties.

The removal of unwanted heat is a frequently encountered problem.Conventional solutions include cooling fans, ice packs and refrigerationsystems. In the latter, a working fluid is compressed (condensed) andpumped into an expansive chamber or pipe system where it evaporates,pulling heat from the atmosphere to satisfy its needed latent heat ofvaporization, and thus cooling the surrounding environment. Air blownthrough the heat exchanger may be cooled and circulated to cool largervolumes such as in domestic and automotive air conditioning systems.

Active cooling (refrigeration) typically requires complex equipmentincluding pumps, valves, compressors, etc. Many refrigeration systemsrequire the use of CFCs (Freon), which is considered hazardous orenvironmentally unfriendly. An evaporative cooling system with a highthermal conductivity medium would offer a simpler, lower costalternative. There is a need for portable coolers which are lightweightand inexpensive so as to be deployed in the field or in third worldcountries.

The thermally conductive carbon foam of this invention overcomes thelimitations of the prior art.

In addition, the present invention relates to porous carbon foam filledwith phase change materials and encased to form a heat sink product, andmore particularly to a process for producing them.

There are currently many applications that require the storage of largequantities of heat for either cooling or heating an object. Typicallythese applications produce heat so rapidly that normal dissipationthrough cooling fins, natural convection, or radiation cannot dissipatethe heat quickly enough and, thus, the object over heats. To alleviatethis problem, a material with a large specific heat capacity, such as aheat sink, is placed in contact with the object as it heats. During theheating process, heat is transferred to the heat sink from the hotobject, and as the heat sink's temperature rises, it “stores” the heatmore rapidly than can be dissipated to the environment throughconvection. Unfortunately, as the temperature of the heat sink rises theheat flux from the hot object decreases, due to a smaller temperaturedifference between the two objects. Therefore, although this method ofenergy storage can absorb large quantities of heat in some applications,it is not sufficient for all applications.

Another method of absorbing heat is through a change of phase of thematerial, rather than a change in temperature. Typically, the phasetransformation of a material absorbs two orders of magnitude greaterthermal energy than the heat capacity of the material. For example, thevaporization of 1 gram of water at 100° C. absorbs 2,439 Joules ofenergy, whereas changing the temperature of water from 99° C. to 100° C.only absorbs 4.21 Joules of energy. In other words, raising thetemperature of 579 grams of water from 99° C. to 100° C. absorbs thesame amount of heat as evaporating 1 gram of water at 100° C. The sametrend is found at the melting point of the material. This phenomenon hasbeen utilized in some applications to either absorb or evolve tremendousamounts of energy in situations where heat sinks will not work.

Although a solid block of phase change material has a very largetheoretical capacity to absorb heat, the process is not a rapid onebecause of the difficulties of heat transfer and thus it cannot beutilized in certain applications. However, the utilization of the highthermal conductivity foam will overcome the shortcomings describedabove. If the high conductivity foam is filled with the phase changematerial, the process can become very rapid. Because of the extremelyhigh conductivity in the struts of the foam, as heat contacts thesurface of the foam, it is rapidly transmitted throughout the foam to avery large surface area of the phase change material. Thus, heat is veryquickly distributed throughout the phase change material, allowing it toabsorb or emit thermal energy extremely quickly without changingtemperature, thus keeping the driving force for heat transfer at itsmaximum.

Heat sinks have been utilized in the aerospace community to absorbenergy in applications such as missiles and aircraft where rapid heatgeneration is found. A material that has a high heat of melting isencased in a graphite or metallic case, typically aluminum, and placedin contact with the object creating the heat. Since most phase changematerials have a low thermal conductivity, the rate of heat transferthrough the material is limited, but this is offset by the high energyabsorbing capability of the phase change. As heat is transmitted throughthe metallic or graphite case to the phase change material, the phasechange material closest to the heat source begins to melt. Since thetemperature of the phase change material does not change until all thematerial melts, the flux from the heat source to the phase changematerial remains tO relatively constant. However, as the heat continuesto melt more phase change material, more liquid is formed.Unfortunately, the liquid has a much lower thermal conductivity, thushampering heat flow further. In fact, the overall low thermalconductivity of the solid and liquid phase change materials limits therate of heat absorption and, thus, reduces the efficiency of the system.

SUMMARY OF THE INVENTION

The general object of the present invention is to provide carbon foamand a composite from a mesophase or isotropic pitch such as synthetic,petroleum or coal-tar based pitch.

Another object is to provide a carbon foam and a composite from pitchwhich does not require an oxidative stabilization step.

These and other objectives are accomplished by a method of producingcarbon foam wherein an appropriate mold shape is selected and preferablyan appropriate mold release agent is applied to walls of the mold. Pitchis introduced to an appropriate level in the mold, and the mold ispurged of air such as by applying a vacuum. Alternatively, an inertfluid could be employed. The pitch is heated to a temperature sufficientto coalesce the pitch into a liquid which preferably is of about 50° C.to about 100° C. above the softening point of the pitch. The vacuum isreleased and an inert fluid applied at a static pressure up to about1000 psi. The pitch is heated to a temperature sufficient to cause gasesto evolve and foam the pitch. The pitch is further heated to atemperature sufficientto coke the pitch and the pitch is cooled to roomtemperature with a simultaneous and gradual release of pressure.

In another aspect, the previously described steps are employed in a moldcomposed of a material such that the molten pitch does not wet.

In yet another aspect, the objectives are accomplished by the carbonfoam product produced by the methods disclosed herein including a foamproduct with a smooth integral facesheet.

In still another aspect a carbon foam composite product is produced byadhering facesheets to a carbon foam produced by the process of thisinvention.

Another object of the present invention is to provide a thermallyconductive carbon foam.

Yet another object is to provide a method of producing a cooling effectutilizing a thermally conductive carbon foam.

Still another object is to provide a heat exchanging device employing acarbon foam core.

These and other objectives are accomplished in one embodiment by athermally conductive, pitch-derived carbon foam.

In one aspect the foam has an open cell ligament composition.

In another embodiment, the objectives are accomplished by a method ofproducing a cooling effect wherein a thermally conductive, pitch-derivedcarbon foam is selected. The foam is contacted with an evaporatingliquid, and an evaporation of the evaporating liquid is effected.

In still another embodiment, the objectives are accomplished by a heatexchanging device having a thermally conductive, pitch-derived carbonfoam core. A fluid impermeable coating covers a portion of the foam coreand exposes a portion. The exposed portion. provides access and egressfor an evaporating liquid.

In another aspect, there are upper and lower reservoirs in fluidcommunication with a core and a pumping device in fluid communicationwith the upper and lower reservoir adapted to deliver the evaporatingliquid from the lower reservoir to the upper reservoir.

In still another aspect, the carbon foam is positioned in separatecolumns to provide a cold storage container with spacing between thecolumns.

In yet another aspect, relative motion between the foam and heattransfer fluid is developed in the presence or absence of an evaporativeliquid by moving the foam, thereby accelerating evaporation andincreasing the cooling effect.

Still another object of the present invention is the production ofencased high thermal conductivity porous carbon foam filled with a phasechange material wherein tremendous amounts of thermal energy are storedand emitted very rapidly. The porous foam that has been filled with aphase change material (PCM) will conduct heat to the phase changematerial such that the temperature of the phase change material willremain close to the operating temperature of the device. As heat isadded to the surface, from a heat source such as a computer chip,friction due to re-entry through the atmosphere, or radiation such assunlight, it is transmitted rapidly and uniformly throughout the foamand then to the phase change material. As the material changes phase, itabsorbs orders of magnitude more energy than non-PCM material due totransfer of the latent heat of fusion or vaporization. Conversely, thefilled foam can be utilized to emit energy rapidly when placed incontact with a cold object.

Non-limiting embodiments disclosed herein are a device to rapidly thawfrozen foods or freeze thawed foods, a design to prevent overheating ofsatellites or store thermal energy as they experience cyclic heatingduring orbit, and a design to cool leading edges during hypersonicflight or re-entry from space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a micrograph illustrating typical carbon foam withinterconnected carbon ligaments and open porosity.

FIGS. 2-6 are micrographs of pitch-derived carbon foam graphitized at2500° C. and at various magnifications.

FIG. 7 is a drawing corresponding to a SEM micrograph (shown in FIG. 27)of the foam produced by the process of this invention.

FIG. 8 is a chart illustrating cumulative intrusion volume versus porediameter.

FIG. 9 is a chart illustrating log differential intrusion volume versuspore diameter.

FIG. 10 is a graph illustrating the temperatures at which volatiles aregiven off from raw pitch.

FIG. 11 is an X-ray analysis of the graphitized foam produced by theprocess of this invention.

FIGS. 12A-C are photographs illustrating foam produced with aluminumcrucibles and the smooth structure or face sheet that develops.

FIG. 13A is a schematic view illustrating the production of a carbonfoam composite made in accordance with this invention.

FIG. 13B is a perspective view of the carbon foam composite of thisinvention.

FIGS. 14-16 are charts plotting temperature/time of the carbon foamresulting from the evaporation of a working fluid according to thisinvention.

FIG. 17 is a diagrammatic view illustrating one embodiment employing thecarbon foam of this invention.

FIGS. 18-21 are diagrammatic views illustrating other embodimentsemploying the carbon foam of this invention.

FIG. 22 is section cut of a heat sink device for thawing food usingacetic acid as the phase change material.

FIG. 23 is a section cut of a heat sink to prevent overheating ofsatellites during cyclic orbits.

FIG. 24 is a section cut of a heat sink used on the leading edge of ashuttle orbiter.

FIG. 25 is a chart plotting the thermal conductivity as a function ofdensity for ARA24 mesophase derived graphite foam graphitized at 4°C./min and 10° C./min.

FIG. 26 is a chart plotting the thermal conductivity as a function ofdensity for Conoco mesophase derived graphite foam graphitized at 10°C./min.

FIG. 27 is a photograph taken by SEM imaging of a sample of the carbonfoam of the invention.

FIG. 28 is a photograph taken by SEM imaging of a sample of the carbonfoam of the invention illustrating the open interconnects between cellsand showing how the interconnect diameter is about half that of the celldiameter, typically on the order of 40% to 60% of the cell diameter.

DETAILED DESCRIPTION OF THE INVENTION

In order to illustrate the carbon foam product and composite of thisinvention, the following Examples I-XIX are set forth. They are notintended to limit the invention in any way.

EXAMPLE I

Pitch powder, granules, or pellets are placed in a mold with the desiredfinal shape of the foam. These pitch materials can be solvated ifdesired. In this Example Mitsubishi ARA-24 mesophase pitch was utilized.A proper mold release agent or film is applied to the sides of the moldto allow removal of the part. In this case, Boron Nitride spray and DryGraphite Lubricant were separately used as a mold release agent. If themold is made from pure aluminum, no mold release agent is necessarysince the molten pitch does not wet the aluminum and, thus, will notstick to the mold. Similar mold materials may be found that the pitchdoes not wet and, thus, they will not need mold release. The sample isevacuated to less than 1 torr and then heated to a temperatureapproximately 50 to 100° C. above the softening point. In this casewhere Mitsubishi ARA24 mesophase pitch was used, 300° C. was sufficient.At this point, the vacuum is released to a nitrogen blanket and then apressure of up to 1000 psi is applied. The temperature of the system isthen raised to 800° C., or a temperature sufficient to coke the pitchwhich is about 500° C. to about 1000° C. This is performed at a rate ofno greater than about 5° C./min. and preferably at about 2° C./min. Thetemperature is held for at least 15 minutes to achieve an assured soakand then the furnace power is turned off and cooled to room temperature.Preferably the foam was cooled at a rate of approximately 1.5° C./min.with release of pressure at a rate of approximately 2 psi/min. Finalfoam temperatures for three product runs were 500° C., 630° C. and 800°C. During the cooling cycle, pressure is released gradually toatmospheric conditions. The foam was then heat treated to 1050° C.(carbonized) under a nitrogen blanket and then heat treated in separateruns to 2500° C. and 2800° C. (graphitized) in Argon.

Carbon foam produced with this technique was examined withphotomicrography, scanning electron microscopy (SEM), X-ray analysis,and mercury porisimetry. As can be seen in the FIGS. 2-7, theinterference patterns highlighting the isochromatic regions undercross-polarized light indicate that the struts of the foam arecompletely graphitic. That is, all of the pitch was converted tographite and aligned along the axis of the struts. These struts are alsosimilar in size and are interconnected throughout the foam. This wouldindicate that the foam would have high stiffness and good strength. Asseen in FIG. 7 by the SEM micrograph of the foam, the foam is opencellular meaning that the porosity is not closed. FIGS. 8 and 9 areresults of the mercury porisimetry tests. These tests indicate that thepore sizes are in the range of 90-200 microns.

A thermogravimetric study of the raw pitch was performed to determinethe temperature at which the volatiles are evolved. As can be seen inFIG. 10, the pitch loses nearly 20% of its mass fairly rapidly in thetemperature range between about 420° C. and about 480° C. Although thiswas performed at atmospheric pressure, the addition of 1000 psi pressurewill not shift this effect significantly. Therefore, while the pressureis at 1000 psi, gases rapidly evolved during heating through thetemperature range of 420° C. to 480° C. The gases produce a foamingeffect (like boiling) on the molten pitch. As the temperature isincreased further to temperatures ranging from 500° C. to 1000° C.(depending on the specific pitch), the foamed pitch becomes coked (orrigid), thus producing a solid foam derived from pitch. Hence, thefoaming has occurred before the release of pressure and, therefore, thisprocess is very different from previous art.

Samples from the foam were machined into specimens for measuring thethermal conductivity. The bulk thermal conductivity ranged from 58 W/m·Kto 106 W/m·K. The average density of the samples was 0.53 g/cm³. Whenweight is taken into account, the specific thermal conductivity of thepitch derived foam is over 4 times greater than that of copper. Furtherderivations can be utilized to estimate the thermal conductivity of thestruts themselves to be nearly 700 W/m·K. This is comparable to highthermal conductivity carbon fibers produced from this same ARA24mesophase pitch.

X-ray analysis of the foam was performed to determine the crystallinestructure of the material. The x-ray results are shown in FIG. 11. Fromthis data, the graphene layer spacing (d₀₀₂) was determined to be 0.336nm. The coherence length (La, 1010) was determined to be 203.3 nm andthe stacking height was determined to be 442.3 nm.

The compression strength of the samples were measured to be 3.4 MPa andthe compression modulus was measured to be 73.4 MPa. The foam sample waseasily machined and could be handled readily without fear of damage,indicating a good strength.

It is important to note that when this pitch is heated in a similarmanner, but under only atmospheric pressure, the pitch foamsdramatically more than when under pressure. In fact, the resulting foamis so fragile that it could not even be handled to perform tests.Molding under pressure serves to limit the growth of the cells andproduces a usable material.

EXAMPLE II

An alternative to the method of Example I is to utilize a mold made fromaluminum. In this case two molds were used, an aluminum weighing dishand a sectioned soda can. The same process as set forth in Example I isemployed except that the final coking temperature was only 630° C., soas to prevent the aluminum from melting.

FIGS. 12A-C illustrate the ability to utilize complex shaped molds forproducing complex shaped foam. In one case, shown in FIG. 12A, the topof a soda can was removed and the remaining can used as a mold. Norelease agent was utilized. Note that the shape of the resulting partconforms to the shape of the soda can, even after graphitization to2800° C. This demonstrates the dimensional stability of the foam and theability to produce near net shaped parts.

In the second case, as shown in FIGS. 12B and C employing an aluminumweight dish, a very smooth surface was formed on the surface contactingthe aluminum. This is directly attributable to the fact that the moltenpitch does not wet the surface of the aluminum. This would allow one toproduce complex shaped parts with smooth surfaces so as to improvecontact area for bonding or improving heat transfer. This smooth surfacewill act as a face sheet and, thus, a foam-core composite can befabricated in-situ with the fabrication of the face sheet. Since it isfabricated together as an integral material, no interface joints resultand thermal stresses will be less, resulting in a stronger material.

The following examples illustrate the production of a composite materialemploying the foam of this invention.

EXAMPLE III

Pitch derived carbon foam was produced with the method described inExample I. Referring to FIG. 13A the carbon foam 10 was then machinedinto ablock 2″×2″×½″. Two pieces 12 and 14 of a prepeg comprised ofHercules AS4 carbon fibers and ICI Fibirite Polyetheretherkeytonethermoplastic resin also of 2″×2″×½″ size were placed on the top andbottom of the foam sample, and all was placed in a matched graphite mold16 for compression by graphite plunger 18. The composite sample washeated under an applied pressure of 100 psi to a temperature of 380° C.at a rate of 5° C./min. The composite was then heated under a pressureof 100 psi to a temperature of 650° C. The foam core sandwich panelgenerally 20 was then removed from the mold and carbonized undernitrogen to 1050° C. and then graphitized to 2800° C., resulting in afoam with carbon-carbon facesheets bonded to the surface. The compositegenerally 30 is shown in FIG. 13B.

EXAMPLE IV

Pitch derived carbon foam was produced with the method described inExample I. It was then machined into a block 2″×2″×½″. Two pieces ofcarbon-carbon material, 2″×2″×½″, were coated lightly with a mixture of50% ethanol, 50% phenolic Durez© Resin available from OccidentalChemical Co. The foam block and carbon-carbon material were positionedtogether and placed in a mold as indicated in Example III. The samplewas heated to a temperature of 150° C. at a rate of 5° C./min and soakedat temperature for 14 hours. The sample was then carbonized undernitrogen to 1050° C. and then graphitized to 2800° C., resulting in afoam with carbon-carbon facesheets bonded to the surface. This is alsoshown generally at 30 in FIG. 13B.

EXAMPLE V

Pitch derived carbon foam was produced with the method described inExample I. The foam sample was then densified with carbon by the methodof chemical vapor infiltration for 100 hours. The density increased to1.4 g/cm³, the flexural strength was 19.5 MPa and the flexural moduluswas 2300 MPa. The thermal conductivity of the raw foam was 58 W/m·K andthe thermal conductivity of the densified foam was 94 W/m·K.

EXAMPLE VI

Pitch derived carbon foam was produced with the method described inExample I. The foam sample was then densified with epoxy by the methodof vacuum impregnation. The epoxy was cured at 150° C. for 5 hours. Thedensity increased to 1.37 g/cm³ and the flexural strength was measuredto be 19.3 MPa.

It is obvious that other materials, such as metals, ceramics, plastics,or fiber reinforced plastics could be bonded to the surface of the foamof this invention to produce a foam core composite material withacceptable properties. It is also obvious that ceramics, or glass, orother materials could be impregnated into the foam for densification.

Based on the data taken to date from the carbon foam material, severalobservations can be made and the important features of the inventionare:

1. Pitch-based carbon foam can be produced without an oxidativestabilization step, thus saving time and costs.

2. High graphitic alignment in the struts of the foam is achieved upongraphitization to 2500° C., and thus high thermal conductivity andstiffniess will be exhibited by the foam, making them suitable as a corematerial for thermal applications.

3. High compressive strengths should be achieved with mesophasepitch-based carbon foams, making them suitable as a core material forstructural applications.

4. Foam core composites can be fabricated at the same time as the foamis generated, thus saving time and costs.

5. Rigid monolithic preforms can be made with significant open porositysuitable for densification by the Chemical Vapor Infiltration method ofceramic and carbon infiltrants.

6. Rigid monolithic preforms can be made with significant open porositysuitable for activation, producing a monolithic activated carbon.

7. It is obvious that by varying the pressure applied, the size of thebubbles formed during the foaming will change and, thus, the density,strength, and other properties can be affected.

The following alternative procedures and products can also be effectedby the process of this invention:

1. Fabrication of preforms with complex shapes for densification by CVIor Melt Impregnation.

2. Activated carbon monoliths.

3. Optical absorbent.

4. Low density heating elements.

5. Firewall Material.

6. Low secondary electron emission targets for high-energy physicsapplications.

It will thus be seen that the present invention provides for themanufacture of pitch-based carbon foam for structural and thermalcomposites. The process involves the fabrication of a graphitic foamfrom a mesophase or isotropic pitch which can be synthetic, petroleum,or coal-tar based. A blend of these pitches can also be employed. Thesimplified process utilizes a high pressure high temperature furnace andthereby, does not require an oxidative stabilization step. The foam hasa relatively uniform distribution of pore sizes (≈100 microns), verylittle closed porosity, and density of approximately 0.53 g/cm³. Themesophase pitch is stretched along the struts of the foam structure andthereby produces a highly aligned graphitic structure in the struts.These struts will exhibit thermal conductivities and stiffniess similarto the very expensive high performance carbon fibers (such as P-120 andK1100). Thus, the foam will exhibit high stiffness and thermalconductivity at a very low density (≈0.5 g/cc). This foam can be formedin place as a core material for high temperature sandwich panels forboth thermal and structural applications, thus reducing fabricationtime.

By utilizing an isotropic pitch, the resulting foam can be easilyactivated to produce a high surface area activated carbon. The activatedcarbon foam will not experience the problems associated with granulessuch as attrition, channeling, and large pressure drops.

The high thermal conductivity carbon foam of the invention may beutilized to provide an evaporatively cooled heat sink or heat exchanger.The carbon foam, as derived from mesophase pitch and as depicted inFIGS. 2-7, has an open structure which allows free access to a workingfluid to the cell walls/ligaments. When the working fluid contacts thecell surface it evaporates, and the latent heat of vaporization causescooling of the carbon foam. The extent of cooling depends upon theworking fluid and the ambient conditions (temperature and pressure). Theheat sink/exchanger temperature has been shown to fall to less than 223K(−50° C.) using acetone as the working fluid at a pressure of 1200microns Hg (1.2 torr), and 0.5° C. using acetone as the working fluid atambient temperature and pressure. Forced air flow over the carbon foamincreases the temperature drop in excess of that observed under ambientconditions. The heat sink/exchanger described herein finds applicationsin heat removal systems such as personal/body cooling suits, portablerefrigeration systems or coolers, and air conditioning systems(household and automotive).

The following Examples demonstrate the evaporative cooling effect on thepreviously described carbon foam when contacted with different workingfluids as represented by acetone, ethanol and water. These Examples arenot intended to limit the invention in any way. The foamed carbon wasdoused or partially immersed in the working fluid. Upon removal from theworking fluid, and as indicated in Examples VII-X, the foam sample wasplaced in a vacuum furnace with a thermocouple penetrating the foamsample. The foam temperature was monitored as a function of time andpressure (vacuum). The ambient laboratory temperature was approximately21° C.

EXAMPLE VII

Acetone

Time(minutes) Pressure(Torr) Temperature(° C.) 0 740 13.5 1 29 −37.5 229 −46.7 3 1.2 −51.8 4 1.2 −53.4

When the sample was removed from the vacuum furnace it was noted thatice had formed, presumably from moisture condensed from the furnaceatmosphere, or desorbed from the foam.

EXAMPLE VIII

Ethanol

Time(minutes) Pressure(Torr) Temperature(° C.) 0 740 20.5 1 29 5.3 2 29−14.7 3 1.2 −21.7 4 1.2 −25.1 5 1.1 −26.8 6 1.0 −28.6

EXAMPLE IX

Water

Time(minutes) Pressure(Torr) Temperature(° C.) 0 740 20.5 1 29 16.4 2 2916.5 3 29 16.6 4 29 14.6 5 29 12.9 6 29 10.5 7 29 2.6 8 29 −1.5 9 29−5.5

In the instance of Example IX the sample was immersed in water in vacuumto ensure that the foam was saturated. This probably allowed an excessof water to penetrate the sample and reduced the exposed foam surfacearea available for evaporation. Moreover, the resultant high waterpartial pressure in the furnace made it impossible to attain good vacuumin a reasonable time. Consequently, the experiment was repeated inExample X, but with substantially less water applied to the foam.

EXAMPLE X

Water (Repeat)

Time(minutes) Pressure(Torr) Temperature(° C.) 0 740 19.9 1 29 14.5 2 290.3 3 29 −5.5

In this case, sub-zero temperatures were attained in a much shorter timethan for Example IX.

The data for Examples VII, VIII and X are plotted in FIG. 14. The lowesttemperature observed (−53.4°) was attained in 4 minutes using acetone asthe working fluid. Temperatures of −24.1° C. and −5.5° C. were attainedover the same time period when the working fluid was ethanol and water,respectively.

A further series of tests as set forth in Examples XI-XIII wereperformed to show the effect of evaporative cooling at atmosphericpressure and temperature. The foamed carbon sample was placed in a petridish. A thermocouple was located in a hole machined into the foam. Thecarbon foam was doused with the working fluid until the bottom of thepetri dish was completely covered with the working fluid. The resultantfoam temperature was then noted as a function of time.

EXAMPLE XI

Acetone

Time Time(minutes) Temperature(° C.) (minutes) Temperature(° C.) 0 21.719 3.4 1 15.7 20 3.2 2 13.6 21 3.0 3 11.5 22 2.9 4 10.3 23 2.7 5 8.9 242.6 6 8.0 25 2.4 7 7.3 26 2.3 8 6.6 27 2.1 9 6.1 28 2.0 10 5.7 29 1.8 115.3 30 1.6 12 4.9 31 1.4 13 4.5 32 1.3 14 4.3 33 1.1 15 4.1 34 1.0 163.9 35 0.8 17 3.7 36 0.7 18 3.5 37 0.6 38 0.5

After 38 minutes there was no acetone visible in the petri dish or underthe carbon foam sample. The sample was placed in an air circulating ovenat 60° C. to dry it and then allowed to cool to ambient temperture.

EXAMPLE XII

Ethanol

Time Time(minutes) Temperature(° C.) (minutes) Temperature(° C.) 0 21.619 15.4 1 20.3 20 15.3 2 19.6 21 15.1 3 19.0 22 15.0 4 18.6 23 15.0 518.1 24 14.9 6 17.8 25 14.8 7 17.4 26 14.8 8 17.1 27 14.8 9 16.9 28 14.710 16.7 29 14.7 11 16.5 30 14.6 12 16.3 31 14.6 13 16.2 32 14.6 14 16.033 14.5 15 15.8 34 14.5 16 15.7 35 14.4 17 15.6 36 14.4 18 15.5 37 14.438 14.3

After 38 minutes there was a significant amount of ethanol visible inthe bottom of the petri dish. The sample was placed in an aircirculating oven at 60° C. to dry it and then allowed to cool to ambienttemperature.

EXAMPLE XIII

Water

Time Time(minutes) Temperature(° C.) (minutes) Temperature(° C.)  0 20.919 19.3  1 20.3 20 19.3  2 20.2 21 19.3  3 20.1 22 19.2  4 19.9 23 19.2 5 19.8 24 19.1  6 19.7 25 19.1  7 19.6 26 19.1  8 19.5 27 19.1  9 19.528 19.1 10 19.5 29 19.1 11 19.5 30 19.0 12 19.5 31 19.0  13* 19.5 3219.0 14 19.4 33 19.0 15 19.4 34 18.9 16 19.3 35 18.9 17 19.3 36 18.9 1819.3 37 18.9 38 18.9 *Additional water squirted over carbon foam sample.

After 38 minutes there was a significant amount of water visible in thebottom of the petri dish. The temperature of the carbon foam plotted asa function of time is shown in FIG. 15. The minimum temperatures arehigher for all three working fluids than in the previous Examples whereevaporation occurred under vacuum. Moreover, the rate of temperaturedecrease was much smaller for all three of the working fluid underambient conditions. The lowest temperature reached (0.5° C.) wasattained in 38 minutes with acetone as the working fluid. The lowesttemperatures attained over similar time periods were 14.3° C. and 18.9°C. for ethanol and water, respectively.

A third series of tests were conducted to determine the effect on foamtemperature of enhanced air flow during the evaporative cooling process.The procedure set forth in the previous Example was followed, exceptthat in this series of experiments a fan (rotary, electric motor drivendomestic cooling type) was used to blow ambient air across the foam andpetri dish.

EXAMPLE XIV

Acetone with Forced Air Flow

Time Time(minutes) Temperature(° C.) (minutes) Temperature(° C.) 0 21.54 −2.8 1 5.2 5 −3.2 2 −0.9 6 −3.5 3 −2.9 7 −3.7

Petri dish was frequently replenished with additional acetone.

EXAMPLE XV

Ethanol with Forced Air Flow

Time Time(minutes) Temperature(° C.) (minutes) Temperature(° C.) 0 21.16 9.1 1 14.6 7 8.9 2 11.5 8 8.7 3 10.8 9 8.8 4 9.7 10 8.9 5 9.3

Ethanol in Petri dish replenished once.

EXAMPLE XVI

Water with Forced Air Flow

Time Time(minutes) Temperature(° C.) (minutes) Temperature(° C.) 0 21.18 15.0 1 18.7 9 14.9 2 17.1 10 14.8 3 16.5 11 14.8 4 15.9 12 14.7 5 15.613 14.7 6 15.3 14 14.7 7 15.1 15 14.6

The data from Examples XIV, XV, and XVI are plotted in FIG. 16. Anenhanced cooling effect is obtained when air is forced over theevaporating working fluid/carbon foam.

Table I below summarizes the temperature drops (differences) attainedfor each working fluid under the three sets of conditions employed.

TABLE I Summary of temperature drop data for the three conditionsexamined here. Temperature Drop, ° C. Ambient Pressure Working FluidVacuum and Forced Air Flow Ambient Pressure Acetone 66.9 25.2 21.2Ethanol 49.1 12.4 7.3 Water 26 6.5 2.0

The temperature drops recorded in the above Table I for a vacuumrepresent extreme conditions. Lower temperature drops would be attainedif intermediate vacuum pressures were used, as indicated by the ambientdata. Forced air flow enhanced the cooling effect due to evaporationbecause the partial pressure of the evaporated solvent over the foam wasreduced, and the saturated air was being constantly purged with fresh(unsaturated) air.

These data clearly demonstrate that the carbon foam of this inventionreadily attains very low temperatures, due to the evaporative coolingeffect of the working fluid, which can be used for the removal ofunwanted heat. The three example working fluids employed in the Exampleswere selected because of their availability. An ideal working fluidwould have a high latent heat of vaporization, a vaporizationtemperature close to ambient, be non-toxic and environmentallyacceptable.

The foam material of this invention attains low temperatures for severalreasons: (i) It is an efficient heat transfer medium because of itsexcellent thermal conductivity and large surface area; (ii) The workingfluid has a high latent heat of vaporization and a low temperature(close to room temperature); (iii) The ambient pressure is low (i.e., avacuum) causing rapid evaporation from the carbon foam surface.

The following are descriptions of preferred embodiments of heat removalsystems for different applications that take advantage of the lowtemperature attained in the foam of this invention through evaporativecooling:

An evaporatively cooled heat sink or air conditioner for home orautomobile is illustrated in FIG. 17 generally at 110. A working fluidis pumped from a reservoir 112 to a header tank 114 via pump 116 andlines 15 and 17. It drains through the carbon foam 118 of this inventionwhich is encased in a impermeable coating or skin 120. The downward flowof fluid through the foam 118 occurs under the influence of gravity or apressure differential created by the pump 116. Evaporation of theworking fluid from the carbon foam surface causes cooling of the carbonfoam. 118. A vacuum in the reservoir 112 created by pump 116 enhancesevaporative cooling from the foam 118 and increase the temperature drop,as demonstrated in the previous Examples VII-XVI. A fan with a motor 22and duct 24 directs a separate air stream (at ambient temperature) fromthe air used for evaporation through penetrations 26 in the coating orcasing 120 and foam core 118 where the air gives up excess heat to thecooled foam core 118. The air therefore exits the foam core 118 at belowambient temperature where it may be ducted to cool inhabited space.Condensers or cold traps 28 may be required to condense vapor exitingthe foam core 118. The condensed working fluid is returned to the headertank 114.

Alternatively, instead of air another cooling fluid, such as water,ethylene glycol, helium or nitrogen could be used to remove heat fromcritical components, such as electronics or chemical/medicines in coldstorage, or internal combustion engines.

FIG. 18 shows an evaporatively cooled cold box generally 130. Anencapsulated carbon foam core 32 surrounds a series of open cavities 36into which items to be cooled are placed. The encapsulating skin 38 alsoprovides enclosed cavities 40 and 42 above and below the foam core 32.The working fluid is poured into the top closed cavity 40 such asthrough opening 44 and drains through the foam 32. Vents 46 areadditionally located in the top cavity allowing the working fluid toevaporate to the atmosphere. Evaporation of the working fluid from thecarbon foam 32 surface reduces the foam's temperature. Heat foradditional working fluid evaporation is extracted from the open cavities36, thus reducing the temperature within the cavities. The entire coldbox is wrapped or clad in the thermal insulation and a thermallyinsulated lid 48 seals the open (cold storage) cavities. A fan could befitted to the insulated cold box 130 to increase air flow through thefoam and thus increase the evaporation rate of the working fluid.

An evaporatively cooled cold pack could also be made with the carbonfoam. It would be somewhat similar to those currently available that arefrozen prior to use, and may be fabricated using the carbon foammaterial. A carbon foam block would be encapsulated with a impermeablematerial. The working fluid would be poured in, wet the foam surface andevaporate, causing the foam temperature to drop. An opening throughwhich the working fluid would be poured would also allow the evaporatingfluid to vent to atmosphere.

FIG. 19 shows the carbon foam 118 of this invention in the form of ablock 51 to be used as an automobile radiator generally 50. Hot enginecooling fluid is introduced into intake manifold 52 connected to pipes54 which pass through the foam block 51 to the output manifold 56. Asseen in FIG. 20 foam block 51 is supported in an automobile as indicatedat 58 having the usual frame 53 and wheels 55. Hot fluid is conveyed byoutput conduit 57 from engine 59 to intake manifold 52. Cooled fluidreturns to engine 59 by intake conduit 60 from output manifold 56. Asthe automobile 58 is moving down the road, air is forced through thefoam block 51 and removes the heat to the environment. The efficiency ofheat transfer from the radiator 50 to the ambient air is directlyrelated to the surface area of the block 51. Since a foam block 2 feetby 2 feet by 1 inches has approximately 19,000 m² of surface area whilea typical radiator may approach 10 m², the increased efficiency of theradiator will improve by roughly 3 orders of magnitude.

FIG. 21 shows the carbon foam 118 in the form of a spinning disk devicegenerally 70. The disk device includes a foam disk portion 72 connectedwith a double walled conduit 74 providing a central hollow conduitmember 76 and an outer conduit member 78. Air and an evaporative fluidare introduced into conduit 78 where it passes into the foam diskportion 72. The air and evaporative fluid are spun out of the diskportion 72 as it is rotated to the outside of the disk portion 72. Thisis shown by arrow 80 for the air and arrow 82 for the evaporativeliquid. A fluid impermeable coating 79 provides a sealed surface onopposing sides of the disk portion 72. Hot fluid to be cooled is passeddown central hollow conduit member 76 where it is cooled in disk portion72. It flows out the bottom of conduit 76 as indicated at 84. Thespinning disk portion 72 is supported by the bearings 86 and 88 in asuitable housing. Rotation of disk portion 72 is effected by motor 90driving pulleys 92 and 94 by drive belt 96 with pulley 94 connected toconduit 74.

It will thus be seen that through the present invention there isprovided:

(i) A carbon foam having a very high thermal conductivity. Largetemperature gradients are thus unlikely to develop, and the surfacecooling due to evaporation will be quickly translated to bulk materialcooling.

(ii) The foam has an extended surface area resulting from its cellularstructure. This allows for rapid evaporation of the working fluid.

(iii) The foam has an open structure which allows the working fluid topermeate the material.

(iv) The cell size and ligament properties may be varied, allowing thematerial to be tailored to the selected working fluid or anticipatedcooling application.

(v) A working fluid may be selected that is non-toxic andenvironmentally acceptable.

(vi) Evaporative cooling systems such as those disclosed hereinpotentially offers low (zero) energy consumption and increasedreliability with few or no moving parts.

Another object of the present invention is the production of a carbonfoam heat sink product, i.e., encased high thermal conductivity porouscarbon foam filled with a phase change material wherein tremendousamounts of thermal energy are stored and emitted very rapidly. Theporous foam is filled with a phase change material (PCM) at atemperature close to the operating temperature of the device. As heat isadded to the surface, from a heat source such as a computer chip,friction due to re-entry through the atmosphere, or radiation such assunlight, it is transmitted rapidly and uniformly throughout the foamand then to the phase change material. As the material changes phase, itabsorbs orders of magnitude. more energy than non-PCM material due totransfer of the latent heat of fusion or vaporization. Conversely, thefilled foam can be utilized to emit energy rapidly when placed incontact with a cold object.

Non-limiting embodiments disclosed herein are a device to rapidly thawfrozen foods or freeze thawed foods, a design to prevent overheating ofsatellites or store thermal energy as they experience cyclic heatingduring orbit, and a design to cool leading edges during hypersonicflight or re-entry from space.

In order to illustrate the carbon foam heat sink product of thisinvention, the following examples are set forth. They are not intendedto limit the invention in any way.

EXAMPLE XVII

Device for Thawing Food

Acetic acid has a heat of melting of 45 J/g at a melting point of 11° C.The heat of melting of food, primarily ice, is roughly 79 J/g at 0° C.Therefore, take a block of foam and fill it with liquid acetic acid atroom temp. The foam will be encased in a box made from an insulatingpolymer such as polyethylene on all sides except the top. The top of thefoam/acetic acid block will be capped with a high thermal conductivityaluminum plate that snaps into place thus sealing the foam/acetic acidinside the polymer case (illustrated in FIG. 22). If the foam block is10-in.×15-in.×0.5-in. thick, the mass of foam is 614 grams. The mass ofacetic acid that fills the foam is roughly 921 grams. Therefore, when apiece of frozen meat is placed in contact with the top of the aluminumblock, the foam will cool to the freezing point of the acetic acid (11°C.). At this point, the heat given off from the acetic acid as itfreezes (it also remains at 11° C.) will be equivalent to 49 KJ. Thisheat is rapidly transferred to the frozen meat as it thaws (it alsoremains at 0° C). This amount of heat is sufficient to melt roughly 500grams (1 lb.) of meat.

EXAMPLE XVIII

Heat Sink to Prevent Overheating of Satellites During Cyclic Orbits

Produce a carbon-carbon composite with the foam in which the foam is acore material with carbon-carbon face sheets (FIG. 23). Fill the foamcore with a suitable phase change material, such as a paraffin wax, thatmelts around the maximum operating temperature of the satellitecomponents. One method to perform this would be to drill a hole in onesurface of the carbon-carbon face sheets and vacuum fill the phasechange material in the liquid state into the porous foam. Once filled,the sample can be cooled (the phase change material solidifies) and thehole can be plugged with an epoxy or screw-type cap. The epoxy and anyother sealant must be able to withstand the operating temperature of theapplication. The foam-core composite will then be mounted on the side ofthe satellite that is exposed to the sun during orbit. As the satelliteorbits the earth and is exposed to the sun, the radiant energy from thesun will begin to heat the composite panel to the melting point of thephase change material. At this point, the panel will not increase intemperature as the phase change material melts. The amount of radiantenergy the panel can absorb will be dependent on the thickness and outerdimensions of the panel. This can be easily calculated and designedthrough knowledge of the orbit times of the satellite such that thematerial never completely melts and, thus, never exceeds the melttemperature. Then, when the satellite leaves the view of the sun, itwill begin to radiate heat to space and the phase change material willbegin to freeze. The cycle will repeat itself once the satellite comesinto view of the sun once again.

EXAMPLE XIX

Heat Sink for Leading Edges

Currently, the shuttle orbiter experiences extreme heats during reentry.Specifically, the leading edges of the craft can reach 1800° C. and thebelly of the craft can reach temperatures as high as 1200° C. If a foamcore composite panel is placed at the surface of the leading edges andat the surface of the belly (FIG. 24), it would be able to absorb enoughenergy to dramatically reduce the maximum temperature of the hot areas.This also would permit a faster re-entry or (steeper glide slope) andmaintain the current maximum temperatures. In this case the phase changematerial would most likely be an alloy, e.g. germanium-silicon, whichmelts around 800-900 C. and does not vaporize until much higher than themaximum temperature of the craft.

For example, Germanium has a heat of formation (heat of melting) of 488J/g. This would require 1.0 Kg of Germanium to reduce the temperature of1 Kg of existing carbon/carbon heat-shield by 668° C. In other words, ifthe existing carbon-carbon were replaced pound-for-pound with germaniumfilled foam, the maximum temperature of the heat shield would only beabout 1131° C. instead of about 1800° C. during re-entry, depending onthe duration of thermal loading.

This U.S. patent application incorporates by reference in theirentireties the following: U.S. patent application Ser. No. 08/921,875filed Sep. 2, 1997; U.S. patent application Ser. No. 08/923,877 filedSep. 2, 1997; U.S. patent application Ser. No. 09/093,406 filed Jun. 8,1998; and U.S. patent application Ser. No. 09/458,640 filed Dec. 9,1999; Klett, J., “High Thermal Conductivity, Mesophase Pitch-DerivedGraphitic Foam,” 43^(rd) Int'l SAMPE Symposium, May 31-Jun. 4, 1998(Aneheim, Calif.); J. Klett, C. Walls and T. Burchell, “High ThermalConductivity Mesophase Pitch-Derived Carbon Foams: Effect of Precursoron Structure and Properties,” Carbon '99, 24^(th) Biennial Conference onCarbon Jul. 11-16, 1999; J. Klett, “High Thermal Conductivity, MesophasePitch-Derived Graphitic Foams,” J., Composites in Mfg., 15:4, pp.1-7(1999); J. Klett, and T. Burchell, “High Thermal Conductivity, MesophasePitch Derived Carbon Foam,” Science and Technology of Carbon, ExtendedAbstracts and Eurocarbon Programme, vol. II, Strasbourg, France, Jul.5-9, 1998; and pages published at the web site of Poco Graphite, Inc. ofDecatur, Tex., at the Internet address poco.com/pocofoam/grafprod, asdownloaded on Jan. 21, 2000.

Thermal Conductivity and Specific Thermal Conductivity: The validity ofthe flash diffusivity method and whether the open porosity would permitpenetration of the heat pulse into the sample had to be established.Deep penetration of the pulse in samples typically causes a change inthe characteristic heat pulse on the back face of the sample. Thus,errors in the reported diffusivity can be as high as 20%. However, therather large struts and small openings of the foam limits the depth ofpenetration to about one to two pore diameters (250-500 micrometers), orless than 2% penetration. Therefore, it was believed that this techniquewould yield a fairly accurate value for the thermal conductivity. Thiswas confirmed by testing samples with both the flash diffusivity methodand the thermal gradient method. The measured conductivities varied byless than 5%, verifying the flash method as a viable method to measurethese foams. If the pore structure changes significantly, the flashmethod will likely yield inaccurate results.

In another embodiment of the invention, two different precursors wereused to produce foam with the process of the invention. These precursorswere a Conoco Mesophase Pitch and a Mitsubishi ARA24 Mesophase Pitch(herein referred to as Conoco and ARA24). The results are shown inTables II and III. They were processed with varying operating pressuresunder nitrogen atmosphere, a heating rate during the foaming step of3.5° C./min, coked at 630° C. for 1 hour, and cooled at the naturalcooling rate of the furnace. The samples were carbonized in a separatefurnace under nitrogen at a heating rate of 0.2° C./min up to 1000° C.and then some samples were graphitized at 2800° C. in yet anotherfurnace at two different heating rates (10° C./min and 4° C./min, TableIII).

The thermal conductivity (a term which is herein used synonymously with“bulk thermal conductivity”) of the foam was very high as shown in TableII and FIGS. 25 and 26. The thermal conductivity of the graphitizedARA24 foam, graphitized at 4° C./min, was in the range of approximately146 to 187 W/m·K, as shown in Table III. This is remarkable for amaterial with such a low density of approximately 0.56 g/cm³. Thiscalculates as a specific thermal conductivity (thermal conductivitydivided by the density) in the range of approximately 256 to 334W·cm³/m·°K·gm. As stated earlier, for a foam with a bulk thermalconductivity of approximately 58 W/m·K, the ligament thermalconductivity is approximately 700 W/m·K. However, with the data shown inTables II and III, when the thermal conductivity of the foam is about147 W/m·K, the ligament thermal conductivity is approximately 1800 W/m·Kand for a foam thermal conductivity approximately 187 W/m·K, theligament thermal conductivity is approximately 2200 W/m·K.

It is an unusual property of the invention that the thermal conductivityof this graphitic carbon foam is substantially isotropic, and ispreferably completely isotropic. The foam exhibits substantiallyisotropic thermal conductivity comparable to the isotropic thermalconductivity of some metallic thermal management materials (Table IV).The foam exhibits a thermal conductivity, 146 to 187 W/m·K for the ARA24foam in Table III, that is comparable to the in-plane thermalconductivity of other carbon-based thermal management materials, such asthe carbon-carbon composites containing carbon fiber that are listed inTable IV, which are 109 W/m·K and 250 W/m·K. The foam has asignificantly higher thermal conductivity in the out-of-plane directionthan these carbon-carbon composites, which are 1 W/m·K and 20 W/m·K.Carbon-based thermal management materials typically exhibit substantialdifferences between in-plane and out-of-plane thermal conductivity, asshown in Table IV. Although several of the other thermal managementmaterials have higher in-plane thermal conductivities, their densitiesare much greater than the foam, i.e., the specific thermal conductivityof the foam is significantly greater than all the available thermalmanagement materials. In fact, the specific thermal conductivity is morethan seven times greater than copper (45 W·cm³/m·°K·gm), the preferredmaterial for heat sinks in the prior art. It is clear that, for thermalmanagement,where weight is a concern or where un-steady state conditionsoccur often, the graphitic foam is superior to most other availablematerials. The advantage of isotropic thermal and mechanical propertiesshould allow for novel designs that are more flexible and moreefficient.

TABLE II Properties of Carbon Foam Samples of the Invention Max SpecificSpecific Heat Treatment Foaming Mean Pore Surface Thermal Thermal PitchTemperature Pressure Total Pore Area Diameter* Density AreaConductivity** Conductivity Sample ID Precursor [° C.] [Psi] [m²/g][microns] [g/cm³] [m²/m³] [W/m · K] [W · cm³/m · K · gm] G AR 1000 40061.979 0.22 13,635,380 0.6 2.7 A AR 1000 600 47.89 125 0.37 17,719,3001.2 3.2 M AR 1000 800 70.31 168 0.44 30,936,400 1.3 3.0 P AR 1000 1000 0.036 90.7 0.54    19,440 1.7 3.1 F Conoco 1000 400 0.956 59.44 0.33  315,480 0.9 2.7 E Conoco 1000 600 0.166 46.93 0.4    66,400 1 2.5 DConoco 1000 800 20.317 28.6 0.49  9,955,330 1.3 2.7 B Conoco 1000 1000 20.565 24 0.56 11,516,400 1.2 2.1 N AR 2800 400 0.025 340 0.25    6,25050 200.0 K AR 2800 600 112.4 165 0.39 43,836,000 72 184.6 L AR 2800 80060.81 100.2 0.48 29,188,800 105 218.8 O AR 2800 1000  0.045 100.85 0.57   25,650 149 261.4 Q AR 2800 1000  0.57 I Conoco 2800 400 0.087 59.190.35    30,450 40.8 116.6 J Conoco 2800 600 0.162 48.45 0.4    64,80085.1 212.8 H Conoco 2800 800 0.15 41.23 0.49    73,500 104.2 212.7 CConoco 2800 1000  27.06 31.3 0.59 15,965,400 134.1 227.3 *note: The meanpore diameter, since it was calculated from results by mercuryporisimetry, is not representative of average cell size. **note: Thermalconductivity was calculated from the measured thermal diffusivity usinga xenon pulse flash diffusivity technique.

TABLE III Thermal Conductivity and Specific Thermal Conductivity vs.Density for Mesophase Derived Graphite Foams Made from DifferentPrecursors in the Invention. Thermal *Specific Thermal GraphitizationDensity Conductivity Conductivity Rate [g/cm³] [W/m-K] [W-cm³/m-K-gm] [°C./min] Conoco 0.59 134.1 227 10 0.56 92.1 164 10 0.56 80.1 143 10 0.54102 189 10 0.53 99 187 10 0.49 104.2 213 10 0.43 85.2 198 10 0.4 84.1210 10 0.4 85.1 213 10 0.32 55.1 172 10 0.36 40.9 114 10 0.35 40.8 11710 ARA24 0.56 187 334 4 0.59 183 310 4 0.62 180 290 4 0.56 177 316 40.58 170 293 4 0.61 169 277 4 0.56 166 296 4 0.56 165 295 4 0.6 161 2684 0.61 160 262 4 0.59 157 266 4 0.62 152 245 4 0.59 151.2 256 4 0.6  150250 4 0.57 148.9 261 4 0.57 146 256 4 0.6 136 227 10 0.6 131.6 219 100.51 127 249 10 0.53 127 240 10 0.52 121 233 10 0.47 119.6 254 10 0.53118 223 10 0.57 112 196 10 0.48 105.3 219 10 0.48 104.5 218 10 0.57 98172 10 0.51 98 192 10 0.49 94 192 10 0.52 93 179 10 0.38 92.2 243 100.45 86.8 193 10 0.55 85.3 155 10 0.4 75 188 10 0.39 74.5 191 10 0.3968.2 175 10 0.29 67.1 231 10 0.28 62 221 10 0.31 55.2 178 10 0.3 52.6175 10 0.25 50.5 202 10 0.27 48.3 179 10 *Specific Thermal Conductivity= Thermal Conductivity divided by Density.

TABLE IV Specific Thermal Thermal Conductivity Conductivity DensityIn-plane Out-of-plane In-plane Out-of-plane Material [gm/cm³] [W/m · K][W/m · K] [W · cm³/m · ° K. · gm] [W · cm³/m · ° K. · gm] Typical 2-D1.88 250 20 132  10.6 Carbon—Carbon EWC-300/Cyanate 1.172 109 1 63 0.6Ester Copper 8.9 400 400 45 45 Aluminum 6061 2.8 180 180 64 64 Aluminum0.19 — ˜10 — 52 Honeycomb 0.5  12 12 24 24 Aluminum Foam

Based on the data in Tables II, III, and IV and in FIGS. 25 and 26, itcan be seen that the carbon foams of the invention, when graphitized,have surprisingly high thermal conductivity and specific thermalconductivity. The graphitic carbon foams typically have a thermalconductivity of at least 40 W/m·°K and/or a specific thermalconductivity at least equal to copper, i.e., at least 45 W·cm³/m·°K·gm,and usually on the order of at least 75 W·cm³/m·K·gm. More typicalgraphitic carbon foams of the invention have a thermal conductivity ofat least 75 W/m·°K and/or a specific thermal conductivity of at least100 W·cm³/m·°K·gm. In the preferred embodiment, the carbon foams of theinvention have a thermal conductivity of at least 100 W/m·K and/or aspecific thermal conductivity of at least 150 W·cm³/m·°K·gm. Morepreferred embodiments contemplate carbon foams having a thermalconductivity of at least 125 W/m·°K and/or a specific thermalconductivity of at least 175 W·cm³/m·°K·gm. Yet more preferredembodiments contemplate carbon foams having a thermal conductivity of atleast 150 W/m·°K and/or a specific thermal conductivity of at least 200W·cm³/m·°K·gm. Still more highly preferred embodiments contemplatecarbon foams having a thermal conductivity of at least 175 W/m·°K and/ora specific thermal conductivity of at least 250 W·cm³/m·°K·gm, with thedata in Tables II-IV and FIGS. 25 and 26 showing that specific thermalconductivities on the order of at least 275 W·cm³/m·°K·gm, and even atleast 300 W·cm³/m·°K·gm, and indeed even at least 325 W·cm³/m·°K·gm, areattainable. Pore diameters indicated in Table II were measured by themercury porisimetry method.

Specific Surface Area: Another property that affects the overall thermalperformance of the carbon foam is the specific surface area (SSA),calculated by:

SSA[m²/m³]=Total Pore Area[m²/g]×Density[g/cm³]×1,000,000[cm³/m³]

Smaller specific surface areas indicate a lower foam pororsity whichreduces the effect of the natural convective heat transfer mode (laminarflow) and allows the more efficient conductive heat transfer mode todominate thermal performance. Larger SSA's enhance evaporative coolingvia increased surface area to volume ratio and increasing the contactarea between the evaporative fluid and the foam material, SSA is also anindicator of the foam's response to forced convective heat transfer(turbulent flow) via fluid passing through the media by increasing thesurface area used for heat transfer.

As shown in Table II, the SSA value for the graphitized carbon foams ofthe invention (heat treated to 2800° C.) was.at least about 6,000 m²/m³,typically above 25,000 m²/m³, and even more typically above 65,000m²/m². SSA values of at least 100,000 m²/m³ or at least 500,000 m²/m³are contemplated in the invention. Indeed, several samples shown inTable II were above 1,000,000 m²/m³, and in the preferred embodiment,the carbon f6am has an SSA of at least about 2,000,000 m²/m³, morepreferably at least about 5,000,000 m²/m³, more preferably still atleast about 10,000,000 m²/m³, and most preferably, at least about15,000,000 m²/m³, with SSA values of at least about 25,000,000 m²/m³ orat least about 35,000,000 also being contemplated. The upper possiblelimit on the SSA value is currently unknown, and while the data in TableII show the highest value achieved with the few samples therein testedas 43,836,000 m²/m³, values both higher or lower than this value arecontemplated as within the invention.

Evaporative Cooling: Examples VII, VIII, and X, along with FIG. 14 showthat the still air experiments in a vacuum furnace produced thefollowing cooling rates:

I. Using acetone as the fluid, the carbon foam temperature reached−53.4° C. (C) in no more than about 4 minutes;

II. Using ethanol as the fluid, the carbon foam temperature reached−28.6° C. in no more than about 6 minutes;

III Using water as the fluid, the carbon foam temperature reached −5.5°C. in no more than about 3 minutes.

Examples XI, XII, and XIII, along with FIG. 15, show that the naturalconvection experiments conducted under ambient room temperatureconditions produced the following cooling rates:

I. Using acetone as the fluid, the carbon foam temperature reached 0.5°C. in no more than 38 minutes;

II. Using ethanol as the fluid, the carbon foam temperature reached14.3° C. in no more than 38 minutes; and

III. Using water as the fluid, the carbon foam temperature reached 18.9°C. in no more than 38 minutes.

As indicated above, the foregoing information was derived from the datapresented with respect to the experiments previously described showingdecreases in temperature with time using acetone, ethanol, and water,respectively. But these are by no means the only conclusions that can bedrawn from the tabular data set forth for these experiments. Forexample, in Example VII it is shown, under the conditions of theexperiment, that, when acetone was the fluid, the carbon foam reached atemperature of −46.7° C. in no more than 2 minutes at a reduced pressure(vacuum) of 29 torr. Similarly, in Experiment VIII it is shown, underthe conditions of the experiment, that, when ethanol was the fluid, thecarbon foam reached a temperature of −21.7° C. in no more than 3 minutesat a reduced pressure (vacuum) of 1.2 torr. And again similarly, inExperiment XI, with acetone as a fluid, and under the natural convectionconditions of the experiment, the carbon foam reached a temperature of5.7° C. in no more than 10 minutes. These and similar conclusions may bedrawn from the tabular data in Examples VII to XVI, which dataillustrate the combined effects the high thermal conductivity and SSAproperties of the carbon foam of the invention have upon the coolingrate achievable with acetone, ethanol, and water, respectively.

X-ray Analysis: Lattice parameters were determined from the indexeddiffraction peak positions (Table V). The X-ray method for crystallitesize determination is well known to those skilled in the art. The 002and 100 diffraction peak breadths were analyzed using the Scherrerequation to determine the crystallite dimensions in the a- andc-directions.$t = \frac{0.9\lambda}{B\quad {\cos \left( {2\theta} \right)}}$

where t is the crystallite size, λ is the X-ray wavelength, B is thebreadth of the diffraction peak [full width half maximum (FWHM) minusthe instrumental breadth], and 2θ is the diffraction angle. As shown inTable V, the 002 peak (which is characteristic of interlayer spacing),was very narrow and asymmetric, indicative of highly ordered graphite.The interlayer spacing calculated with the Scherrer method is in therange of approximately 0.3354 nm to 0.3364 nm. The crystallite size inthe c-direction was calculated from these data to be at leastapproximately 82.4 nm, and the 100 peak (or 1010 in hexagonalnomenclature) was used to calculate the crystallite size in thea-direction of at least approximately 21.5 nm. These crystallite sizesare larger than typical high thermal conductivity carbon fibers andtherefore, the foam ligaments should perform similarly to high orderpyrolytic carbon and high thermal conductivity carbon fibers such asK1100 and vapor grown carbon fibers (VGCF).

TABLE V X-ray Diffraction Data for Carbon Foam Samples Max Heat PitchTreatment Foaming d₀₀₂ Narrowness Relative *Sample Pre- TemperaturePressure spacing La Lc Peak Angles (2θ) FWHM Peak Split Factor ID cursor[° C.] [Psi] [nm] [nm] [nm] 002 101 100 002 101 100 (RPSF) original AR1000 1000  0.3362 20.3 44.2 26.4853 42.3185 44.2751 0.2940 0.5540 1.28700.470 N AR 2800 400 0.3364 11.8 48.2 26.4769 42.1512 44.1507 0.22920.7644 0.8856 0.413 K AR 2800 600 0.3362 17.8 46.6 26.4839 42.091144.2000 0.2348 0.5374 0.7207 0.298 L AR 2800 800 0.3360 21.5 79.326.5006 42.1416 44.2069 0.1628 0.4542 0.7807 0.299 O AR 2800 1000 0.3356 21.4 56.7 26.5540 42.2270 44.2815 0.1590 0.5220 0.7438 0.308 Q AR2800 1000  0.3354 18.4 82.4 26.5383 42.3065 44.2815 0.2040 0.4568 0.74380.304 *Samples N-Q of Table V are the same as samples N-Q of Table II,respectively.

The “doublet” at the 100 and 101 peaks is characterized by a relativepeak split factor (RPSF) parameter, or narrowness, calculated using thepeak angles and the full width half maximums (FWHM). The equation is:$\quad^{*}{RPSF} = \frac{\left( {\frac{{FWHM}_{101}}{2} + \frac{{FWHM}_{100}}{2}} \right)}{{2\theta_{100}} - {2\theta_{101}}}$

A smaller RPSF indicates closer peaks at 100 and 101 and favorablelattice conditions for thermal conductivity and structural integrity.The data reported in Table V shows values for RPSF no greater than0.470, with the lowest reported value for a carbon foam heat treated at2800° C. being 0.298 and the highest being 0.413.

Microstructural Characterization: FIGS. 27 and 28 are scanning electronmicrographs of the pore structure of a foam sample of the invention. Thefoam exhibits a structure having open interconnects 205 between cells(or pores) 200, with such cells (or pores) being of similar geometricshape, typically ellipsoidal, and sometimes spherical or essentiallyspherical. (It is noted that a sphere is a specific form of anellipsoid.) It is evident from the images that the graphitic structureis oriented parallel to the cell walls and highly aligned along the axisof ligaments 210. This highly aligned structure is significantlydifferent from typical vitreous carbon foams: vitreous carbon foams arevoid of graphitic structure, have large openings and linear ligaments,and are mostly pentagonal dodcahedral in shape.

Moreover, it can be seen that in the junctions 220 between ligaments,the graphitic structure is less aligned and possesses more foldedtexture. It is postulated that this arises from the lack of stresses atthis location during forming. Therefore, the well-ordered structure inthese regions is primarily an artifact of the structure in precursormesophase prior to heat treatment.

We claim:
 1. A carbon foam having a thermal conductivity of at least 40W/m·°K.
 2. A carbon foam as defined in claim 1 having a thermalconductivity of at least 50 W/m·°K.
 3. A carbon foam as defined in claim1 having a thermal conductivity of at least 75 W/m·°K.
 4. A carbon foamas defined claim 1 having a thermal conductivity of at least 100 W/m·°K.5. A carbon foam as defined in claim 1 having a thermal conductivity ofat least 125 W/m·°K.
 6. A carbon foam as defined in claim 1 having athermal conductivity of at least 150 W/m·°K.
 7. A carbon foam as definedin claim 1 having a thermal conductivity of at least 175 W/m·°K.
 8. Acarbon foam as defined in claim 2, 4, 5, or 7 having a maximum thermalconductivity of about 187 W/m·°K.
 9. A carbon foam as defined in claim 7having a maximum thermal conductivity of about 187 W/m·°K.
 10. A carbonfoam as defined in claim 1, 3, 7, or 9 having a specific thermalconductivity of at least 100 W·cm³/m·°K·gm.
 11. The carbon foam of claim10 having a specific surface area of at least 65,000 m²/m³.
 12. A carbonfoam as defined in claim 1, 3, 7 or 9 having a specific thermalconductivity of at least 300 W·cm³/m·K·gm.
 13. A carbon foam as definedin claim 1, 5, or 9 having a specific thermal conductivity of at least150 W·cm³/m·K·gm.
 14. A carbon foam as defined in claim 1, 3, 7 or 9having a specific thermal conductivity of at least 200 W·cm³/m·K·gm. 15.A carbon foam as defined in claim 1, 5, 7 or 9 having a specific thermalconductivity of at least 250 W·cm³/m·K·gm.
 16. A carbon foam as definedin claim 1, 5, 7, or 9 having a specific thermal conductivity in therange from about 114 to about 334·Wcm³/m·K·gm.
 17. A carbon foam asdefined in claim 1, which, when initially at a room temperature ofapproximately 21° C. and saturated with acetone at said roomtemperature, cools to about −50° C. in no more than about 4 minutes whenplaced under a reduced pressure (vacuum) approximately equivalent to 1.2torr.
 18. A carbon foam as defined in claim 1, which, when initially ata room temperature of approximately 21° C. and saturated with ethanol atsaid room temperature, cools to about −28° C. in no more than about 6minutes when placed under a reduced pressure (vacuum) approximatelyequivalent to 1.0 torr.
 19. A carbon foam as defined in claim 1, which,when initially at a room temperature of approximately 21° C. andsaturated with water at said room temperature, cools to below 0° C. inno more than about 3 minutes when placed under a reduced pressure(vacuum) approximately equivalent to 29 torr.
 20. A carbon foam asdefined in claim 1, which, when initially at a room temperature ofapproximately 21° C. and saturated with acetone at said roomtemperature, cools to about 1.0° C. in no more than about 34 minuteswhen exposed to ambient conditions under natural evaporation.
 21. Acarbon foam as defined in claim 1, which, when initially at a roomtemperature of approximately 21° C. and saturated with ethanol at saidroom temperature, cools to about 15° C. in no more than about 23 minuteswhen exposed to ambient conditions under natural evaporation.
 22. Acarbon foam as defined in claim 1, which, when initially at a roomtemperature of approximately 21° C. and saturated with water at saidroom temperature, cools to about 19° C. in no more than about 33 minuteswhen exposed to ambient conditions under natural evaporation.
 23. Thecarbon foam of claim 1 having a specific surface area of at least 6000m²/m³.
 24. The carbon foam of claim 23 having a specific surface area ofat least 65,000 m²/m³.
 25. The carbon foam of claim 16 having a specificsurface area of at least 500,000 m²/m³.
 26. The carbon foam of claim 23having a specific surface area of at least 500,000 m²/m³.
 27. The carbonfoam of claim 23 having a specific surface area of at least 1,000,000m²/m³.
 28. The carbon foam of claim 13 having a specific surface area ofat least 1,000,000 m²/m³.
 29. The carbon foam of claim 23 having aspecific surface area of at least 5,000,000 m²/m³.
 30. The carbon foamof claim 23 having a specific surface area of at least 15,000,000 m²/m³.31. The carbon foam of claim 14 having a specific surface area of atleast 20,000,000 m²/m³.
 32. The carbon foam of claim 23 having aspecific surface area of at least 30,000,000 m²/m³.
 33. A carbon foam asdefined in claim 14 having an X-ray diffraction pattern characterized bydoublet 100 and 101 peaks characterized by a relative peak split factorno greater than about 0.470.
 34. A carbon foam as defined in claim 16having an X-ray diffraction pattern characterized by doublet 100 and 101peaks characterized by a relative peak split factor no greater thanabout 0.413.
 35. A carbon foam as defined in claim 34 wherein said X-raydiffraction pattern is further characterized by a full width halfmaximum for the 002 peak angle of between about 0.159 and about 0.294degrees.
 36. A heat exchange device comprising as a heat transfersurface the carbon foam of claim
 7. 37. An evaporatively cooled heatsink comprising the carbon foam of claim
 7. 38. The carbon foam of claim1 containing micropores containing a phase change material.
 39. A carbonfoam as defined in claim 1 having a density from about 0.4 to about 0.65gm/cm³.
 40. A carbon foam as defined in claim 1 having a density fromabout 0.55 to about 0.60 gm/cm³.
 41. A carbon foam as defined in claim 1having a density from about 0.50 to about 0.65 gm/cm³.
 42. A carbon foamas defined in claim 1 having a mean pore diameter no greater than about340 microns.
 43. A carbon foam as defined in claim 1 having a mean porediameter no greater than about 60 microns.
 44. A carbon foam as definedin claim 1 characterized by an X-ray diffraction pattern exhibitingrelatively sharp doublet peaks at 2θ angles between 40 and 50 degrees.45. A carbon foam as defined in claim 1 characterized by an X-raydiffraction pattern having an average d002 spacing of about 0.336.
 46. Acarbon foam as defined in claim 1 characterized by an X-ray diffractionpattern having an average d002 spacing of 0.336.
 47. A carbon foam asdefined in claim 1 having an open cell pore structure substantiallycomprised of ellipsoidal pores.
 48. A carbon foam as defined in claim 1having an open cell pore structure consisting essentially ofsubstantially ellipsoidal pores.
 49. A carbon foam as defined in claim 1having an open cell pore structure comprised of pores whose planarcross-sectional images are substantially circular or elliptical.
 50. Acarbon foam as defined in claim 1 having an open cell pore structureconsisting essentially of pores whose planar cross-sectional images aresubstantially circular or elliptical.
 51. A carbon foam as defined inclaim 1 of substantially open cell structure comprising cell wallswherein carbon derived from a mesophase pitch is substantially alignedalong the cell wall axes, said carbon foam having been non-oxidativelystabilized.
 52. A carbon foam as defined in claim 51 wherein said carbonsubstantially aligned along the cell wall axes is substantially in theform of graphite.
 53. A carbon foam as defined in claim 1 characterizedby being essentially completely graphitic and being furthercharacterized by an open cell structure substantially comprised ofellipsoidal pores and by graphite substantially aligned along the axesof the cell walls.
 54. A carbon foam as defined in claim 1 having a porestructure consisting essentially of pores having diameters within a 100micron range.
 55. A carbon foam as defined in claim 1 having an X-raydiffraction pattern substantially as depicted in FIG.
 11. 56. A carbonfoam having a specific thermal conductivity of at least 125W·cm³/m·K·gm.
 57. A carbon foam as defined in claim 56 having a specificthermal conductivity of at least 175 W·cm³/m·K·gm.
 58. A carbon foam asdefined in claim 56 having a specific thermal conductivity of at least225 W·cm^(3/)m·K·gm.
 59. A carbon foam as defined in claim 56 having aspecific thermal conductivity of at least 275 W·cm³/m·K·gm.
 60. A carbonfoam as defined in claim 56 having a specific thermal conductivity of atleast 325 W·cm³/m·K·gm.
 61. A carbon foam as defined in claim 56 havinga maximum specific thermal conductivity of about 334 W·cm³/m·K·gm. 62.The carbon foam of claim 9, 23, or 61 having a specific surface area ofat least 25,000 m²/m³.
 63. The carbon foam of claim 7, 23, or 61 havinga specific surface area of at least 100,000 m²/m³.
 64. A carbon foam asdefined in claim 2, 4, 6, 57, 59, 23, 24, 26, or 30 having an X-raydiffraction pattern characterized by doublet 100 and 101 peakscharacterized by a relative peak split factor no greater than about0.470.
 65. The carbon foam of claim 3, 9, 56, 61 or 23 having a specificsurface area of at least 10,000,000 m²/m³.
 66. The carbon foam of claim3, 9, 23, or 57 having a specific surface area of at least 25,000,000m²/m³.
 67. The carbon foam of claim 9, 23, or 61 having a specificsurface area of at least 35,000,000 m²/m³.
 68. The carbon foam of claim23, 27, or 29 having a specific surface area no greater than about44,000,000 m²/m³.
 69. The carbon foam of claim 25 having a specificsurface area no greater than about 44,000,000 m²/m³.
 70. A carbon foamas defined in claim 63 having an X-ray diffraction pattern characterizedby doublet 100 and 101 peaks characterized by a relative peak splitfactor no greater than about 0.470.
 71. A carbon foam as defined inclaim 65 having an X-ray diffraction pattern characterized by doublet100 and 101 peaks characterized by a relative peak split factor nogreater than about 0.470.
 72. A carbon foam as defined in claim 69having an X-ray diffraction pattern characterized by doublet 100 and 101peaks characterized by a relative peak split factor between about 0.298and about 0.413.
 73. A carbon foam as defined in claim 5, 7, 56, 58, 60,61, 27, or 29 having an X-ray diffraction pattern characterized bydoublet 100 and 101 peaks characterized by a relative peak split factorbetween about 0.298 and about 0.470.
 74. A carbon foam as defined inclaim 72 wherein said X-ray diffraction pattern is further characterizedby a full width half maximum for the 002 peak angle of between about0.159 and about 0.2292 degrees.
 75. A carbon foam as defined in claim 2,7, 57, 60, 61, 23, or 27 characterized by an X-ray diffraction patternhaving a full width half maximum for the 002 peak angle of between about0.159 and about 0.294 degrees.
 76. A carbon foam as defined in claim 75in which the X-ray diffraction pattern is further characterized by (a)doublet 100 and 101 peaks further characterized by a relative peak splitfactor between about 0.298 and about 0.470, and (b) a d002 spacingbetween about 0.3354 and about 0.3364.
 77. A carbon foam as defined inclaim 76 having a mean pore diameter between about 30 and about 60microns, and a density between about 0.2 and about 0.65 gm/cm³, and arelative peak split factor no greater than about 0.413.
 78. A carbonfoam as defined in claim 1 or 23 having a mean pore diameter no greaterthan 60 microns and a density between about 0.2 and about 0.65 gm/cm³.79. A carbon foam having an X-ray diffraction pattern characterized by afull width half maximum for the 002 peak angle of between about 0.159and about 0.294 degrees.
 80. A carbon foam having an X-ray diffractionpattern characterized by doublet 100 and 101 peaks characterized by arelative peak split factor no greater than about 0.470.
 81. Apitch-derived carbon foam which provides a thermal conductivity of atleast 40 W/m·K with an open cell pore structure substantially comprisedof pores of similar geometric shape.
 82. A carbon foam as defined inclaim 81 having struts interconnected throughout the carbon foam.
 83. Acarbon foam as defined in claim 81 whose open cell pore structureconsists essentially of pores whose planar cross-sectional images are ofsubstantially the same geometric shape.
 84. A carbon foam as defined inclaim 83 wherein said cross-sectional images are substantially circularor elliptical.